Jquery-livequery is a project mainly written in JavaScript, it's free.
A fork of the original http://plugins.jquery.com/project/livequery
Live Query utilizes the power of jQuery selectors by binding events or firing callbacks for matched elements auto-magically, even after the page has been loaded and the DOM updated.
The Live Query plugin is dual licensed (just like jQuery) under the MIT and GPL licenses.
Copyright (c) 2008 Brandon Aaron